People
have always wanted to explore the sea, to look for sunken
treasure, to salvage wrecks, to bring up marine products
like pearls and sponges, or to simply examine the beautiful
underwater world.

Oceanography is a branch of science that studies all
aspects of the ocean's physical features and inhabitants. It
is the study of anything about the oceans: the description
of land surrounding them, the plants and animals that live
in them, how the oceans affect humans, and how humans affect
the oceans. Oceanography is not a separate science but
encompasses many sciences, such as biology, chemistry,
geology, physics and geography.

The scientists and explorers of earlier times could only
guess what lay below the waves. Now, underwater instruments
and machines can tell us. Some devices tell us about the
water itself. Research ships lower bottles that fill with
water at different levels in the sea; thermometers fixed to
the bottles measure the temperature at these levels. Ships
tow bathythermographs to record how underwater temperature
and pressure change across an ocean. Complicated devices
called bathysondes measure underwater saltiness, temperature
pressure and the speed of underwater sounds. In order to
learn how underwater currents flow, researchers use special
buoys and floats that send back signals to the surface.

The dark, cold depths of the ocean pose a huge challenge
for underwater exploration but sophisticated sonar systems
and manned submersibles developed since World War I allow
the deep-sea floor to be observed first-hand by
scientists.

Collecting information about an object or phenomenon from
a distance is the essence of remote sensing. It combines
sophisticated sensor technology with the processing
capabilities of high-powered computers. The vast wealth of
data derived from satellites show considerable environmental
detail at regional and global scales.